In recent years, an adhesive in the form of a film has been used as a die bonding material in use for adhesion between semiconductor elements such as IC or LSI, or adhesion of semiconductor elements to supporting members, instead of an adhesive in the form of a paste that has been used from the past. In particular, in a high-density surface-mounting semiconductor device having a small mounting area such as a chip-sized package, a stack package, a system in package or the like, an adhesive in the form of a film which is excellent in the thickness accuracy or in the projection controllability as compared to an adhesive film in the form of a paste has been widely applied.
With this recent high-density mounting trend, thinning of a semiconductor element has been advanced. An adhesive in the form of a film is attached to a wafer having a thickness of not more than 100 μm at a state that a surface protecting tape to be used when grinding finely is attached, in order to prevent breakage of the wafer.
When the adhesion temperature in the adhesion process is high, a surface protecting tape having a low heat resistance is thermally deformed, causing the wafer to bend. So, a big defect occurs when the wafer is carried back into a cartridge or the wafer is conveyed. For that reason, an adhesive in the form of a film having a property capable of adhering at a much lower temperature (hereinafter referred to as adhesiveness at a low temperature) has been in demand.
As for an adhesive in the form of a film having excellent adhesiveness at a low temperature which can be applied to this usage, an adhesive comprising a polyimide siloxane having a repeating structural unit represented by the following general formula (3) has been known (refer to JP1993-331444A, U.S. Pat. No. 2,996,857, JP1997-59589A, JP1999-92744A and the like),

wherein, in the formula (3), Y represents a quadrivalent organic group; R1 and R2 represent divalent hydrocarbon groups; R3 and R4 represent monovalent hydrocarbon groups; R1 and R2, and R3 and R4 may each be the same or different; m is an integer of not less than 2; and n is an integer of not less than 1.
It is known that the aforementioned polyimide siloxane can be usually prepared by subjecting a diaminopolysiloxane which is used at least as a diamine component represented by the following general formula (4), and a tetracarboxylic acid dianhydride which is used as an acid dianhydride component represented by the following general formula (5) to an imidization reaction by heating,

wherein, in the formula (4), R1 and R2 represent divalent hydrocarbon groups; R3 and R4 represent monovalent hydrocarbon groups; R1 and R2, and R3 and R4 may each be the same or different; and m is an integer of not less than 2,

wherein, in the formula (5), Y represents a quadrivalent organic group.
The diaminopolysiloxane represented by the above formula (4) is usually obtained by reacting a diaminosiloxane compound represented by the following general formula (6), with a cyclic siloxane represented by the following general formula (7) in the presence of an alkali catalyst,

wherein, in the formula (6), R1 and R2 represent divalent hydrocarbon groups; R3 and R4 represent monovalent hydrocarbon groups; and R1 and R2, and R3 and R4 may each be the same or different,

wherein, in the formula (7), R3 and R4 represent monovalent hydrocarbon groups and may each be the same or different; and I is an integer of not less than 3. Since this reaction is an equilibrium reaction, the cyclic siloxane represented by the general formula (7) necessarily remains in the diaminopolysiloxane represented by the general formula (4) as an impurity.
This remained cyclic siloxane is non-reactive, but its boiling point depends on the molecular weight and the cyclic siloxane having a low molecular weight volatilizes at a relatively low temperature. As a result, the present inventors have found that, when an adhesive in the form of a film comprising polyimide siloxane having a diaminopolysiloxane as a raw material which was not pre-treated for the reduction of the cyclic siloxane was used in the production of a semiconductor device, the cyclic siloxane volatilized by heating in the process, causing defects in some cases.
For example, one of the production processes is a wire bonding process, but in that process, a semiconductor device in the production is exposed to a temperature of from about 150 to 200° C. for several minutes to 1 hour or so. At that time, when the cyclic siloxane having a low boiling point (boiling point of a cyclic trimer: 134° C. and that of a cyclic tetramer: 175° C.) volatilizes, a wire bonding pad part is contaminated, causing some problems. That is, the adhesive strength in the wire bonding is deteriorated or the wire bonding miss occurs.
On the other hand, while the environmental problem has been recently getting serious, the lead free soldering used for adhesion of a semiconductor device to a substrate has been continuously progressed. As a reliable candidate of the lead free soldering, Sn—Ag—Cu type soldering can be cited, which has a melting point of about 220° C., about 40° C. higher than a melting point of the current Sn—Pb type soldering of about 180° C. So, it is said that the surface temperature of a semiconductor device at the time of mounting using lead free soldering reaches 250 to 260° C. For that reason, an adhesive in the form of a film having excellent heat resistance has been in demand for maintaining sufficient adhesive strength even at 260° C.
In order to solve the above problems, an object of the present invention is to provide an adhesive resin composition which can be used for an adhesive in the form of a film exhibiting superior adhesiveness at a low temperature and heat resistance, an adhesive in the form of a film comprising the adhesive resin composition, and a semiconductor device using the adhesive in the form of a film.